#include <bits/stdc++.h>
#define MOD 1000000007
using namespace std;

int sz[100001];
long long fact[100001];

long long cnt(int n, int k) {
	return (fact[n] / fact[k]) / fact[n-k];
}

int main() {
	int n, m; // n - size of field,  m - count of arrays.
	cin >> n >> m;

	fact[0] = 1;
	fact[1] = 1;
	for(long long i = 2; i <= n; i++) fact[i] = (fact[i-1]*i)%MOD;

	for(int i = 0; i < m; i++) {
		cin >> sz[i];
	}

	long long ans = 1;
	for(int i = 0; i < m; i++) {
		ans *= cnt(n, sz[i]);
		n -= sz[i];
	}

	cout << ans << endl;
}